(1) Field to which invention relates
The invention relates to a roller mill comprising a rotary grinding pan and grinding rollers adapted to roll on this grinding pan and which are journalled stationarily though with a provision for vertical pivoting.
(2) The prior art
In the last few decades the power, dimensions and weight of roller mills have substantially grown. This trend particularly affects the transmissions, which have had to be designed for larger and larger loads, since they comprised the axial thrust bearing, which serves for taking up the grinding pressure. In the case of the prior art mill design the grinding forces, produced by the rollers, were taken up by an axial thrust bearing, which was fitted in the housing of a mill transmission. The axial loads have increased in the course of mill development to such a degree that there are constantly more exacting requirements as regards the stiffness of the transmission housing and the degree of precision with which it is machined. Since the transmissions therefore in fact consist of the torque converter as one element and the axial thrust bearing as the other element serving for taking up the grinding pressure, the overloading of only one element has frequently meant the breakdown of the whole system. The precision machining of the transmission housings, which presently reach a weight of up to approximately 100 tons gives rise to exacting requirements in manufacture and considered in isolation in fact represents an excessive cost factor. Even small inaccuracies in manufacture frequently lead to premature breakdown owing to the high loads involved. Transmission have already been in use with operating loads of 575 Mp and dynamic additional loads of 2800 Mp.